Ground-based surveys have used morphological criteria, colour selection and
emission line selection. Lists of blue compact galaxies were pioneered by
Zwicky, followed by Fairall and others who isolated objects from their
anomalous
high surface brightness as seen on the Palomar Sky Survey. Spectroscopic
follow ups have revealed a large proportion of H II galaxies
and AGNs
(Kunth et al. 1981)

The colour selection proceeds by searching for blue or ultraviolet excess
objects involving various techniques such as the use of very low dispersed
images or multiple colour direct images. Dispersed images have been used by the
First and Second Byurakan Survey (FBS, SBS) by
Markarian (1967)
on IIaF emulsion
and later the University Michigan survey (UM,
MacAlpine et al. 1977)
and Case survey
(Pesch and Sanduleak
1983)
with IIIaJ emulsion. The second method has been pioneered by
Haro (1956)
and extensively developed by the Kiso Observatory Survey
(Takase and
Miyauchi-Isobe 1984).
Low resolution slitless spectroscopy enables to detect [O II] 3727,
H, [O III] 4959, 5007 and H
lines depending on the chosen emulsion or filter.
Good seeing and excellent guiding are a requisite to avoid trailing and loss
in detectivity. These techniques face a trade off between the dispersion
and the spectral range covered. The higher the dispersion, the easier it
becomes to detect weak emission lines against the continuum, while a narrow
spectral
range cuts significantly the sky background at the expense of the redshift
range. The recent surveys conducted by
Gallego et al. (1997)
and Salzer (1999)
use the
H line which can be bright even
in low-excitation or very
metal-poor objects. Because each technique involves specific observational
biases, modern surveys tend to combine various approaches. The use
of large CCD arrays equipped with scanning Fabry Perot interferometry or
slitless spectroscopy offer deeper limits at the
expense of the reduced field of view. In the future, these combinations will
probe distant H II galaxies populations. The most difficult problem that these
surveys have to face is that of the follow-up observations
(Terlevich et
al. 1991).
Getting even a
rough oxygen abundance for an object fainter than the 17th magnitude
requires long telescope time and suggests the use of multi-object-spectroscopy.